(1) Field of the Invention
This invention relates to the control of Dutch Elm disease. More particularly the invention concerns a method for regulating the aggregation of the bark beetle Scolytus multistriatus which exploits a mixture of three compounds used alone or in combination with compatible biocides in order to simultaneously attract and combat the beetle.
(2) Description of the Prior Art
Dutch Elm disease has devastated elm populations in the northeastern United States and presently threatens American elms throughout their natural and cultivated range. The smaller European elm bark beetle Scolytus multistriatus (Marsham) is the principal vector for the Dutch Elm disease pathogen, Ceratocystis ulmi.
The need for a strong force which could be harnessed to aggregate this beetle has been apparent for some time. This beetle now ranks among the most pernicious tree destroyers. Wholesale spraying of the habitats of these insects with even the most baneful of pesticides usually proves to be a futile, if not deleterious exercise, since bark beetles spend most of their time safely situated underneath tree bark where they mate and reproduce and rear their young. Indeed, indiscriminate spreading of toxic chemicals may do more harm than good if many other animals predacious of beetles come into contact with the lethal spray deposits while seeking their prey. The predators may thus be deterred if not totally eliminated before they can execute this natural function of capturing and destroying the young beetles of a new brood as they emerge from a tree. Chemical control of this sort has been further complicated by difficulty in locating the beetle infestations before a new brood has dispersed to other areas.
Investigations by Martin (1936).sup.1, Meyer and Norris (1967).sup.2, and Peacock, et al. (1971).sup.3 have shown that adult elm bark beetles are weakly attracted to uninfested elm wood.
Several years ago it was determined that Scolytus produces an aggregation pheromone. Research has thus focused on developing a synthetic simulation of this pheromone which could be used for bait in mortality traps. A pheromone is an animal attractant secretion that affects another of its own species. Typically beetle pheromones serve as chemical messengers directing other beetles to a receptive mate, palatable fare and/or a comfortable place in which to lay eggs. The report by Peacock, et al. (1971) demonstrated that secondary mass attack by both sexes of beetles on potential breeding sites is directed by an aggregation pheromone produced by virgin females boring into the phloemcambial region of weakened elm trees. The chemical composition of this pheromone has until the present time been unknown.